Even cheap mp3s on iTunes cost money, and it can be daunting to a financially challenged music fan to build a library of music that they’re really only curious about and not sure about just yet. In the Essential Download Series, we’ll take a look at groundbreaking and influential artists from each of music’s three classical ages and give you a place to start your own exploration of their music. In today's installment we take a look at the essential Beatles downloads every library should start with.